Statistical Study of Solar Wind, Magnetosheath, and Magnetotail Plasma and Field Properties: 12+Years of THEMIS Observations and MHD Simulations

The solar wind plasma is a major plasma source for the Earth's magnetosphere, which has a strong influence on the magnetotail plasma and field properties. The relative importance of different plasma entry mechanisms and pathways is largely determined by the solar wind conditions. Therefore, the spatial and temporal dependence of magnetotail plasma and field properties under different kinds of solar wind conditions is critically important for understanding the Earth's magnetosphere. This study presents a statistical study of fundamental magnetotail plasma properties in a normalized reference frame by utilizing 12+ years of data from NASA's Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission. These statistical maps are mostly in agreement with the magnetosheath of MHD runs from the CCMC BATS-R-US model, but some features in the maps can be explained by kinetic particle physics, not present in the MHD. The results are also used to investigate the presence of any magnetotail plasma parameter asymmetries and their possible causes. Plain Language Summary Earth's intrinsic magnetic field, generated by the currents in the Earth's interior, protects our planet from solar radiation and plasma called the solar wind. However, physical processes such as magnetic reconnection occurring at the boundary of this magnetic barrier, the magnetosphere, can break this shield, enabling access of solar wind plasma into the Earth's magnetosphere. Earth's ionosphere provides another source for magnetospheric plasma. This plasma can be further accelerated to huge energies, which provides a threat for astronauts and satellites. The effectiveness of physical mechanisms that control the entry and acceleration of this plasma strongly depends on the local magnetic field geometry and plasma properties, which in turn are affected by the solar wind. However, the solar wind properties are not constant but vary as it can originate from different regions of the sun. While the magnetic field of the Sun, the interplanetary magnetic field (IMF), on average forms an "Archimedean Spiral," flapping of the heliospheric current sheet and fluctuations along field lines will make the IMF "hit" the Earth at different orientations, thus impacting the shock geometry in front of the planet, which in turn affects the downstream plasma and field properties in the turbulent boundary layer called the magnetosheath. In this paper, we have characterized the dependence of the large-scale plasma properties in the Earth's magnetosphere and magnetosheath on the solar wind and IMF conditions by using over 12years (thus covering over one solar cycle) of data from NASA's Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission.